In the field of cosmetics, cleansing cosmetics for removing makeup are in the form of creams, milky lotions and liquids, and are available in types consisting of emulsions, oils and aqueous types which are used corresponding to their respective ease of use. However, aqueous types, which contain no or very little oil, had the problem of having weak cleansing strength despite leaving little oily feeling after cleansing. Consequently, liquid cleansing oils have come into the mainstream in recent years which are capable of easily mixing into old makeup and which can be easily rinsed off with water. Cleansing oils are self-emulsifying oily liquid compositions comprised of a mixture of an oily component and a surfactant. These products have the property of rapidly undergoing a phase inversion when contacted with water, and first involve the migration of old makeup into an oily component as a result of mixing between the cleansing cosmetic and makeup, followed by the formation of an oil-in-water emulsion by the oily component containing old makeup as a result of contact with water, and finally removing the makeup by rinsing with water (see, for example, patent document 1). Since this type of self-emulsifying composition forms an emulsion simultaneous to contact with water, cleansing strength and feel during use are poor when the skin is wet, thereby making this unsuitable for use in the bathroom. On the other hand, a technology has also been disclosed for demonstrating cleansing strength even when in contact with water by containing a polyvalent alcohol or water in addition to an oily component and a surfactant (see, for example, patent document 2). However, since it is necessary for this type of cleansing composition to incorporate numerous types and large amounts of components other than oil, it had the problem of decreased cleansing strength as compared with typical cleansing oils.
Next, bathing cosmetics prevent damaged skin, cracked skin and chapped skin, and are frequently used during bathing to improve skin condition. Examples of the forms of bathing cosmetics include bath salts, bath oils and herbs. In particular, self-emulsifying, oily bath oil type products comprised of a mixture of an oily component and a surfactant self-emulsify in hot water when placed in a bath, resulting in the oily component in the form of fine particles being uniformly dispersed in the bathwater, and making it possible for the oily component to demonstrate various type of inherent ameliorative effects possessed thereby such as that of an emollient, moisture retention, anti-inflammatory effects and hot bathing effects. However, since conventional self-emulsifying oily bathing cosmetics comprised of a mixture of an oily component and a surfactant have inadequate dispersivity in hot water, they had the problem of remaining in the form of the bathing cosmetic and being suspended in the water as a result of self-emulsification not occurring. As a result, in addition to having a poor feel on the skin after bathing in the form of unpleasantness during bathing and a damp feeling on the skin, there was also the problem of the bathing cosmetic adhering to the walls of the bathtub.
The formation of a microemulsion during the process of adding water is effective for these problems. Microemulsions are systems in which a greater amount of oil (or water) is solubilized than ordinary micelle solutions (or reverse micelle oily solutions), and are anisotropic solutions having a clear to blue appearance. Similar to ordinary macroemulsions, microemulsions exist in one of two types consisting of oil-in-water (O/W) and water-in-oil (W/O) types, while there are also microemulsions in which an oily phase and aqueous phase, in which large amounts of water and oil are solubilized, are continuous (bicontinuous). Conventional liquid oily cleansing cosmetics and oily bathing cosmetics are either surfactant oily solutions comprising a mixture of a surfactant and an oil, or reverse micelle oily solutions to which an extremely small amount of water has been added, and since these oily solutions are only capable of solubilizing small amounts of water, they undergo phase separation and form a cloudy emulsion when the solubilization limit is exceeded. Consequently, they emulsify instantaneously in the case the hands and so forth are wet, resulting in decreased cleansing strength.
Microemulsions are known to be obtained by adding an auxiliary surfactant in the form of an intermediate alcohol having 5 to 10 carbon atoms to three components consisting of water, surfactant and oil (see, for example, non-patent document 1). However, these intermediate alcohols have been unable to be used in cosmetics or pharmaceuticals due to skin irritation and other problems with safety.
[patent document 1] Japanese Examined Patent Application, Second Publication No. H6-99275
[patent document 2] Japanese Unexamined Patent Application, First Publication No. 2000-327529
[non-patent document 1]J. H. Schulman, W. Stoeckenius and L. M. Prince: J. Phys. Chem., 63, 1677 (1959)